Rumor has it that the younger guy will end up being Azrael or Darkwing at the end of this movie.

Which "younger guy"? There are two of them.

One of them is John Blake which is Bane's real name before he transforms. If you go to the 43 second mark, this is the guy I'm referring to here.

The other character actually isn't even named in the credits and the kid that plays him is only 12 years old. It's possible that it's Dick Grayson and he becomes Robin at the end but if this is the case then why doesn't he have a more prominent appearance in the trailer and his character would be named in the credits. EDIT: I just watched the trailer again more closely
and he doesn't even appear in the trailer at all.

Also keep in mind this is the final movie. They won't introduce a major character such as this right at the end of the movie.